Sim.atomselections no longer triggers Universe build on call

It can be expensive to build some Universes, so we want to be able to
store selections without having it built. This removes a relic from the
old "multiple Universes" scheme, in which the default Universe was
loaded to make it the "active" Universe for any selections work if no
Universe was already active.

CHANGELOG

@@ -13,10 +13,13 @@ The rules for this file:
 
 ------------------------------------------------------------------------------
 
-??/??/16
+??/??/16 dotsdl
 
     * 0.7.0
 
+Changes
+
+    * Sim.atomselections no longer loads Universe on use if not already present
 
 04/04/16 dotsdl, orbeckst, richardjgowers, sseyler
 

src/mdsynthesis/treants.py

@@ -138,15 +138,9 @@ def atomselections(self):
         """Stored atom selections for the universe.
 
         Useful atom selections can be stored for the universe and
-        recalled later. Selections are stored separately for each defined
-        universe, since the same selection may require a different selection
-        string for different universes.
-
+        recalled later.
         """
-        # attach universe if not attached, and only give results if a
-        # universe is present thereafter
-        if self.universe:
-            if not self._atomselections:
-                self._atomselections = limbs.AtomSelections(self)
+        if not self._atomselections:
+            self._atomselections = limbs.AtomSelections(self)
 
-            return self._atomselections
+        return self._atomselections